Power saving compressor and control logic

ABSTRACT

An air conditioner control method may entail measuring an evaporator first temperature at an exit side of the evaporator, maintaining the evaporator first temperature, measuring a length of time that the evaporator maintains the evaporator first temperature, providing a user-set evaporator target temperature; and reducing a rate of refrigerant compressed by a compressor based on a relationship between the length of time that the evaporator maintains the evaporator first temperature and the evaporator target temperature. Furthermore, an air conditioner control method utilizing a condenser and a cold storage unit may entail turning off an air conditioner compressor, maintaining operation of a condenser cooling fan, closing a thermostatic expansion valve, opening a bleed port to bypass the thermostatic expansion valve, and receiving a liquid refrigerant into the cold storage unit from the condenser after the refrigerant passes through a thermostatic expansion valve bleed port and the evaporator.

FIELD

The present disclosure relates to an air conditioning apparatus and amethod of controlling the output of a vehicle air conditioningcompressor based on evaporator utilization.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.Vehicle manufacturers are continuously striving to produce vehicles thatoverall, consume less energy. In many vehicles, specific components suchas alternators, air-conditioning compressors, and cooling fans aredriven by belts and pulleys that rely directly on rotation of theengine, which must consume extra fuel as opposed to a situation wherecomponents are not directly engine-driven. Accordingly, in vehiclesutilizing internal combustion engines and engine-driven components,attention is being directed at improving the efficiency of engine-drivencomponents to reduce fuel consumption.

Stated differently, because current air conditioning system logic doesnot consider controlling other operational points, or that is, other airconditioning components, when the cooling capacity of the evaporator hasbeen reached, the compressor of a current air conditioning system willcontinue to try to cool or make the evaporator colder even when thecapacity of the evaporator has been reached.

Cold storage is an area of technology that is being studied on mildhybrid systems. Mild hybrid systems are systems that occasionally turnoff the engine and thus the air conditioning compressor but also usuallydo not operate the compressor solely on electrical power. Thus,increasing cold storage within the air conditioning system is sought toenable the evaporator to continue to remove heat from air passed throughthe evaporator even after the engine and compressor cease to operate.Utilization of cold storage to prolong evaporator utilization to achieveextended cool air from the exit side of the evaporator is sought to beaccomplished using cooling fan logic. Such will make the air conditionermore efficient.

While efforts at increasing efficiencies may be directed at a variety ofengine-driven components, a further need exists in the art forincreasing the efficiency of air conditioning systems. Morespecifically, what is needed then is a vehicle air conditioningapparatus and a method of controlling the air conditioning apparatusthat pertains to monitoring evaporator capacity and changing the speedand/or the displacement of the compressor according to the evaporatorcapacity. Additionally needed is air conditioning control logic toextend the time of blown cold air from an evaporator based upon thedegree of cold storage within the air conditioning system.

SUMMARY

An air conditioner control method may entail measuring an evaporatorfirst temperature at an exit side of the evaporator, maintaining theevaporator first temperature, measuring a length of time that theevaporator maintains the evaporator first temperature, providing auser-set evaporator target temperature; and reducing a rate ofrefrigerant compressed by a compressor based on a relationship betweenthe length of time that the evaporator maintains the evaporator firsttemperature and the evaporator target temperature. Furthermore, an airconditioner control method utilizing a condenser and a cold storage unitmay entail turning off an air conditioner compressor, maintainingoperation of a condenser cooling fan, closing a thermostatic expansionvalve, opening a bleed port to bypass the thermostatic expansion valve,and receiving a liquid refrigerant into the cold storage unit from thecondenser after the refrigerant passes through a thermostatic expansionvalve bleed port and the evaporator.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a schematic diagram depicting components of a vehicle airconditioning and cooling system;

FIG. 2 is a top view of a vehicle interior depicting locations ofvarious air conditioning components;

FIG. 3 is a flowchart depicting steps of controlling an air conditioningsystem;

FIG. 4 depicts air conditioning components when an air conditionercompressor is compressing;

FIG. 5 depicts air conditioning components when an air conditionercompressor is not compressing;

FIG. 6 is a graph of evaporator outlet temperature versus time for aperiod of time when the compressor is not operating; and

FIG. 7 is a flowchart depicting steps of controlling an air conditioningsystem.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.Turning to the present teachings, cold storage is an area of airconditioner technology that may be utilized or implemented on mildhybrid vehicles. A mild hybrid vehicle is a type of vehicle thatnormally is not configured to operate its air conditioning compressorsolely from electrical power when the internal combustion engine is notoperating, as in a “full hybrid” type of vehicle, because of costconstraints. Therefore, the air conditioning compressor on a mild hybridvehicle is typically only operated from mechanical energy from theengine when the engine is operating and when the engine is notoperating, the compressor does not function. Alternatively, an electriccompressor may be employed, but this again imposes cost constraints.Concerning mild hybrid vehicles, it remains a desire to prolong the coldair that is available from the exit side of the evaporator for as longas possible, including during periods of time when the engine is notfunctioning. Thus, ways of utilizing an air conditioning cold storagecontainer on the vehicle is desired. As is known in the field of vehicleair conditioning, cold storage may be accomplished using a type of wax,such as paraffin that freezes and remains cold until it is needed.Utilizing cold storage containers may also have a savings associatedwith them that are not possible with different arrangements of differenttypes of compressors and ways of powering such compressors when anengine is not operating.

Turning now to FIGS. 1 and 2, details of the teachings of the presentinvention will be discussed. With initial reference to FIG. 1, a blockdiagram of a conventional vehicle heating, ventilating andair-conditioning system (“HVAC”) system 10 is depicted, which may beresident in a vehicle 11. A refrigeration cycle of the vehicle HVACsystem 10 includes an air-cooling system 12. The air-cooling system 12includes a compressor 14 which draws, compresses, and discharges, orpumps, a refrigerant. The power of a vehicle engine 16 is transmitted tothe compressor 14 through pulley 18, pulley 19 and a belt 20. Thevehicle engine 16 drives not only the air conditioning compressor 14 butalso such auxiliaries as an electricity generator or alternator 21, apower steering unit hydraulic pump 23, and a coolant or water pump 25via belts, shafts, chains and other power transmitting devices.

In a refrigeration cycle, the compressor 14 discharges a superheated gasrefrigerant of high temperature and high pressure, which flows into acondenser 22. In the condenser 22, heat exchange is performed with theoutside air 24, which may be assisted or driven by a cooling fan 31,which normally blows forced air 29 at a higher velocity than the outsideair 24, so that the refrigerant is cooled to undergo condensing. Therefrigerant condensed in the condenser 22 then flows into a receiver 26,in which the refrigerant is separated into a gas and a liquid. Aredundant liquid refrigerant in the refrigeration cycle is stored insidethe receiver 26. The liquid refrigerant from the receiver 26 isdecompressed by an expansion valve 28 into a gas-liquid double phasestate of low pressure refrigerant. The low pressure refrigerant from theexpansion valve 28 then flows into an evaporator 30 by way of an inletpipe 32. The evaporator 30 is arranged inside an HVAC case 34 of theHVAC system 10. The low pressure refrigerant flowing into the evaporator30 absorbs heat from the air inside the HVAC case 34 during evaporation.An outlet pipe 36 of the evaporator 30 is connected to the suction sideof the compressor 14 so that the cycle components mentioned aboveconstitute a closed circuit.

Continuing with FIGS. 1 and 2, the HVAC case 34 forms a ventilation duct38 through which air conditioning air is sent into the vehicle cabin orpassenger compartment 40. The HVAC case 34 contains a blower or fan 42that may be arranged on the upstream side 44 of the evaporator 30. Aninside/outside air switch box (not shown) may be arranged on the suctionside 46 of the fan 42 (left of the fan 42 as viewed from FIG. 1). Theair inside the passenger compartment 40 (inside air) or the air outsidethe passenger compartment 40 (outside air) switched and introducedthrough the inside/outside air switch box is sent into the HVAC case 34through the ventilation duct 38 by the fan 42.

The HVAC case 34 accommodates, on the downstream side 48 of theevaporator 30, a hot water heater core 50 to exchange heat with airpassing through the heater core 50. The heater core 50 includes an inletpipe 52 and an outlet pipe 54. An engine coolant, such as water or anantifreeze solution that circulates around the vehicle engine 16, isdirected to the heater core 50 through the inlet pipe 52 by a water pump25. A water valve 58 controls the flow volume of engine coolant suppliedto the heater core 50. A radiator 60 and a thermistor 62 furthercooperate to control the temperature of the flowing coolant.

A bypass channel 66 exists beside the hot water heater core 50 in theHVAC case 34. An air mix door 64 is provided to adjust the volume ratiobetween warm air and cool air that passes through the hot water heatercore 50 and the bypass channel 66, respectively. The air mix door 64adjusts the temperature of the air blown into the passenger compartment40 by adjusting the volume ratio between the warm air and cool air.

Additionally, a face outlet 68, a foot outlet 70, and a front windshielddefroster outlet 72 are formed at the downstream end of the HVAC case34. The face outlet 68 directs air toward the upper body portions ofpassengers, the foot outlet 70 directs air toward the feet of thepassengers, and the defroster outlet 72 directs air toward the internalsurface of a windshield. The outlets 68, 70 and 72 are opened and closedby outlet mode doors (not shown). The air mix door 64 and the outletmode doors mentioned above are driven or adjusted by electric drivingdevices such as servo motors via linkages or the like.

With the inclusion of FIG. 3, a control method 80 of an HVAC system 10in accordance with the present disclosure will be provided. The controlmethod 80 may be employed in the HVAC system 10 as described above, aswill be evident by reference to such in the explanation that follows.Beginning with the start bubble 82, the routine proceeds to inquiryblock 84 to inquire whether the evaporator temperature is stable andgreater than the evaporator target temperature. The evaporatortemperature may be measured in more than one way. For instance, athermistor 85, which is a resistor whose resistance varies in accordancewith its temperature, may be used to measure the temperature of theevaporator 30, such as at the airflow exit surface of the evaporator 30.Similarly, a resistance temperature detector 87 may be used to measurethe temperature at the airflow exit surface of the evaporator 30.Resistance temperature detectors differ from thermistors in that thematerial used in a thermistor is generally a ceramic or polymer, whileresistance temperature detectors use pure metals. Still yet, atemperature probe may be used to measure the temperature of the airflow88 on the exit side of the evaporator 30, such as at the evaporatorsurface, or immediately aft of the evaporator surface, such as withininches from the exit side of the evaporator surface. Therefore, theevaporator temperature may be measured on the evaporator surface orwithin the airflow 88, within inches of the evaporator surface.

Continuing with the inquiry at inquiry block 84, if the evaporatortemperature is stable, that is consistent and not changing, and theevaporator temperature is greater than the evaporator targettemperature, the flow of the control logic proceeds to inquiry block 86.However, if the evaporator temperature is not stable or if theevaporator target temperature is equal to or less than the evaporatortarget temperature, then the flow of control logic returns to thebeginning and re-enters inquiry block 84. Generally, a reason forinquiring as to whether the evaporator temperature is stable is toprevent the deliberate changing of anything in the HVAC system 10, suchas regarding operation of the air conditioning compressor 14, until thechange has been completed. To determine a stable evaporator temperature,a time period, such as 10 seconds, 30 seconds, 1 minute, etc. may be setfor maintaining such a temperature in order for the evaporatortemperature to be considered stable. Continuing, the HVAC system has atarget panel-air temperature that is set by a vehicle operator 92 orother passenger 94 on an air conditioning panel 96 within the passengercompartment 40. Setting the target air temperature sets or fixes thetemperature of the blowing air 98 that exits from the outlets 68, 70 and72 within the passenger compartment 40 after the blowing air has passedthrough the evaporator 30 as airflow 88.

Therefore, setting a temperature on the air conditioning panel 96adjusts the degree of work or compression of the compressor 14. Stateddifferently and in terms of the compressor 14, the compressor 14compresses more or less refrigerant depending upon thetemperature/amount of the air to be blown from the outlets 68, 70 and72. By adjusting the degree of work or compression of the compressor 14with respect to the refrigerant compressed, the amount and/or rate ofrefrigerant passing through the evaporator varies, as well as itstemperature in the evaporator.

At block 86, upon the reply to the inquiry at block 84 being “yes,” acontrol unit 102 in communication with the compressor 14 adjusts oreffects a change in the electrical current supplied to the compressor14, if the compressor is electrically controlled, or adjusts the strokeor displacement of the piston that does the compression or pumping ofthe refrigerant in the compressor 14.

After the compression of the compressor 14 is adjusted (i.e. lessened orreduced in output) by control of the control unit 102, inquiry block 104inquires whether the evaporator temperature has increased (becomewarmer) since the compression of the compressor 14 was adjusted. If theevaporator temperature has not increased, then the control returns tothe inquiry block 84 to again make the inquiry as to whether theevaporator temperature is stable and greater than the evaporator targettemperature. However, if the evaporator temperature has increased(become warmer), then control proceeds to block 106. At block 106, thecompressor speed (current) is increased by the control unit 102 if thecompressor 14 is an electric compressor, or alternatively, the currentinto the compressor may be increased or changed if it is a mechanicalcompressor 14 that has a swash plate, which is changed electrically inconjunction with a control valve. The mechanically driven compressor 14,such as driven by pulleys 18, 19, may be driven by the engine. Uponmaking the adjustment (increase in current or speed) of the compressor14, the evaporator temperature may be decreased, thus resulting incolder air being discharged from the outlets 68, 70 and 72.

By using the above control logic, the work or compression of thecompressor is controlled so that the compressor output or work does notexceed the evaporator capacity. Stated differently, the control logic ofthe present disclosure permits the compressor 14 to be used only up tothe cooling capacity of the evaporator 30. By preventing the compressor14 from compressing faster or from compressing additional refrigerantwhen the evaporator can not be cooled or lowered in temperature, asmeasured at the evaporator surface, vehicle energy is conserved.Conserving vehicle energy may mean conserving gasoline that the internalcombustion engine is consuming to provide the energy necessary tooperate a belt-driven external—variable displacement compressor (E-VDC)at high capacity when such capacity is actually not necessary at thetime that the air conditioning evaporator has reached its coolingcapacity. Alternatively, in the event of an electrically drivencompressor, the electric compressor may reduce its rpm, and thuscapacity, at the time that the air conditioning evaporator has reachedits maximum cooling capacity. A feature of the control logic is that ittakes into consideration operational points where the evaporatorcapacity has been reached and it reduces compressor power consumption inorder to reduce engine fuel consumption during periods when thecompressor is run at excess capacity, which is when the evaporatorcapacity has been reached for example. This strategy actively reducescompressor capacity to match that of the limiting factor, toperformance, in the system.

In order to effectively control the compressor in accordance with thelogic disclosed, the control unit 102 may be in communication with thecompressor 14, whether it is an electric compressor or a belt-drivenE-VDC compressor, the thermistor 85, the resistance temperature detector87, and the surface of the evaporator 30 to determine a temperatureassociated with the evaporator 30. Continuing, the controller 102 mayalso be capable of tracking time intervals between temperature readings.

Continuing now with reference to FIGS. 4 and 5, the components of an airconditioning system 110 and their use to increase air conditionerefficiency when the engine is turned off will be described. FIGS. 4 and5 depict air conditioning components, as presented in FIG. 1, such as acompressor 14, a condenser 22, an evaporator 30, a condenser cooling fan31, and expansion valve 28, also known as a thermal expansion valve.Additionally, because the air conditioning system 110 depicted in FIGS.4 and 5 is one that may be used on a mild hybrid vehicle, a cold storageunit 112 and a bleed orifice 122, also called a bypass orifice 122, maybe utilized. The bleed orifice 122 is essentially a fixed orifice thatbypasses the expansion valve 28, also known as a “TXV” 28 or “thermalexpansion valve” 28.

FIG. 4 depicts a system in which the air conditioning system 110functions with the engine operating to drive an engaged compressor 14 tocondense refrigerant that circulates in the loop depicted with solidarrows 116. With the air conditioning system 110 functioning, the TXV 28also functions. More specifically, the TXV 28 is a temperature type ofexpansion valve that reduces the pressure of the liquid phaserefrigerant from the condenser 22 to expand the liquid phase refrigerantin an isenthalpic manner and includes a valve part and a temperaturesensing part 117, which may be arranged on the refrigerant outflow sideof the evaporator 30. The temperature sensing part 117 is arrangedbetween the evaporator 30 and the cold storage unit 112. A throttleopening part of the TXV 28 may be controlled according to a refrigeranttemperature sensed by the temperature sensing part of the TXV 28. Suchcontrol may bring the degree of superheat of the refrigerant flowing outof the evaporator 30 to a specified value (for example, from 5 degreesC. to 10 degrees C.).

Continuing with the system 110 of FIG. 4, the cold storage unit or tank112 is located between the evaporator 30 and the compressor 14 so as tobe in series with the evaporator 30. Within the cold storage unit 112, acold storage material 118 resides, such as a wax or wax-like material asexamples. Additionally, a cold storage heat exchanger 120 may residewithin the cold storage unit 112. The cold storage heat exchanger 120 isa heat exchanger that causes refrigerant flowing out of the evaporator30 in the tube indicated by solid arrow 116 to be introduced into thecold storage unit 112 and exchange heat between the refrigerant and thecold storage material in the cold storage unit 112. The process of thecold storage unit 112 exchanging heat and becoming colder with thecompressor 14 compressing is known as “charging.” As depicted in FIG. 4,the condenser 22 is filled with liquid refrigerant to a degree, asindicated by the volume 123.

Turning now to FIG. 5, the air conditioning system 110 of FIG. 4 isdepicted, although the system 110 depicted in FIG. 5 functions underdifferent operating parameters or conditions, yet consistent with thosethat may be applicable to a mild hybrid system of a vehicle. FIG. 5depicts a discharging process in which the internal combustion engine 16that drives the compressor 14 with rotational motion is off and thus,the compressor 14 ceases to operate which ceases compression by thecompressor 14. Thus, when the system 110 has its compressor turned off,the system 110 is in a discharge mode, and higher pressure from the highpressure side of the system (between the condenser 22 and the TXVinlet), and lower pressure from the low pressure side of the system(between the evaporator and the cold storage unit 112), will begin tobalance. In taking advantage of such a pressure differential, teachingsof the present disclosure are directed to increasing the amount and timethat liquid refrigerant may be drawn from the condenser 22, through ableed port 122 to bypass the TXV 28, through the evaporator 30, and intothe cold storage unit 112, even after the engine 16 and compressor 14are turned off. Such may be done in conjunction with maintainingoperation of the condenser cooling fan 31. Such movement of liquidrefrigerant is possible because of the pressure differential that existsbetween the condenser 22 and the cold storage unit 112 just after thecompressor 14 is turned off. More specifically, movement of liquidrefrigerant occurs because the pressure is greater in the condenser 22,which is on the high pressure side of the system, than in the coldstorage unit 112, which is on the low pressure side of the system 110.

Continuing, because the tubes through which refrigerant travels, asdepicted by arrows 116, create a closed loop within the air conditioningsystem, any liquid refrigerant 123 in the condenser 22 may still bedrawn through the tubes to the evaporator 30. Thus, maximizing theamount of liquid condensate present in the system, that is, increasingthe amount of liquid refrigerant, after the engine 16 and compressor 14are turned off and getting the condensate to the evaporator 30 may beaccomplished by utilizing the volume of cold storage in the cold storageunit 112.

With continued reference to FIG. 5, when the compressor 14 is turnedoff, the compressor 14 essentially creates a block in the refrigerantline as nothing passes through the compressor 14 after it has beenturned off. Therefore, between the condenser 22 and the compressor 14,refrigerant ceases to flow in the refrigerant line 126 and between thecompressor 14 and the cold storage unit 112, refrigerant ceases to flowin the refrigerant line 128. However, because the contents of the coldstorage unit 112 remain cold for a period of time after the compressor14 ceases to compress, the heat transfer created by such cold storagecan be used to draw remaining liquid refrigerant from the condenser 22.Additionally, even after the engine 16 and compressor 14 are turned off,the cooling fan 31 may remain turning to provide airflow through thecondenser 22. By continuing the operation of the cooling fan 31, heatmay continue to be removed from the condensed refrigerant in thecondenser 22. At the same time, because the mass of cold storagematerial 118 in the cold storage unit 112 is at a temperature, forexample, of 5 degrees Celcius to 10 degrees Celcius, condensedrefrigerant will continue to be drawn from the condenser 22, through thetubes 116, and into the evaporator 30 so that the fan 42 may continue toblow forced air 43 through the evaporator 30. By continuing to drawliquid refrigerant 123 from the condenser 22 and into the evaporator 30,and blowing forced air 43 through the evaporator 30, vehicle occupantswithin a vehicle cabin 40 may continue to enjoy air conditioned air,even after the compressor 14 and engine 16 have been turned off. Suchmay be the case in a mild hybrid vehicle whose engine 16 and compressor14 are turned off at a red light at an intersection or for example, if avehicle is in stop and start traffic, such as in a traffic jam.

To facilitate the drawing of liquid refrigerant from the condenser 22and into the evaporator 30, bleed orifice 122 or bypass orifice 122 maybe utilized in place of the TXV 28. Such bleed orifice 122 or bypassorifice 122 will automatically open and thereby prevent the TXV 28 frombeing utilized when the engine is turned off. Stated differently, theTXV 28 is not utilized when the engine 16 and compressor 14 are turnedoff. As the cold storage unit 112 continues to draw liquid refrigerantfrom the condenser 22 and into the evaporator 30, the amount of liquidrefrigerant 123 in the condenser 22 decreases, as depicted in viewingthe amount of liquid refrigerant 123 in FIG. 4 and the amount of liquidrefrigerant 123 in FIG. 5.

Turning now to FIG. 6, the effects of the teachings of the presentdisclosure will be described. FIG. 6 depicts plots of Evaporator OutletTemperature (Celsius) versus Time (seconds) when an air conditionercompressor 14 is not operating. The “Target” Plot 130 depicts a plot ofa traditional, typical vehicle air conditioner system in which thecompressor stops when the engine stops. That is, no further transfer ofrefrigerant occurs upon turning the engine off. Furthermore, no airconditioning cold storage unit is utilized. Plot 132 depicts theprojected effects of the vehicle air conditioning system of the presentdisclosure. More specifically, the plot 132 crosses the targettemperature level 134 at the point 136 while in a traditional airconditioning system with no cold storage the plot 130 crosses the targettemperature level 134 at 138. As depicted, the teachings of the presentdisclosure result in an increase of blown cold air within the passengercompartment 40 of approximately more than 40 seconds. More specifically,at time 0 seconds, the vehicle engine 16 may be turned off.Approximately 20 seconds later as indicated at a time of 20 seconds, thetarget temperature line 134 is crossed by the plot 130; however, theplot 132 of the present teachings crosses the target temperature line134 at some time beyond 60 seconds. Therefore, the teachings of thepresent invention provide a significant amount of additional time (morethan 40 additional seconds) of blown air, at or below the targettemperature of 15 degrees Celcius, within the vehicle compartment forvehicle occupants to enjoy.

To achieve the results depicted in FIG. 6, the control logic 140 of FIG.7 begins at start block 142 and progresses to inquiry block 144 whichinquires if the air conditioning compressor is operating. If the airconditioning compressor is operating, then the inquiry simply returnsonto itself until the result of the inquiry is “no.” When the result ofthe inquiry at inquiry block 144 is “no,” the control proceeds to block146 where the operation of the condenser cooling fan 31 is maintained.By maintaining operation of the condenser cooling fan 31, liquidrefrigerant in the condenser 30 continues to be transformed from anyrefrigerant vapor in the condenser 30 and the liquid refrigerantcontinues to be cooled by the blown air from the fan 31. Continuing toblock 148, the TXV valve 28 is closed, and then block 150 where thebleed port 122 or bypass tube 122 is opened to permit the liquidrefrigerant in the refrigerant tubes between the condenser 22 and theevaporator 30 to continue to flow. Then at block 152 liquid refrigerantis drawn from the condenser 22 through the evaporator 30 and into thecold storage unit 112 to provide continued flow of refrigerant into theevaporator 30 after the compressor 14 has been turned off or disengaged,such as upon turning off an engine.

Therefore, in addition to the above disclosure, an air conditionercontrol method 80 may entail measuring an evaporator first temperatureat a downstream side 48 of the evaporator 30, maintaining the evaporatorfirst temperature, measuring a length of time, such as with thecontroller 102, that the evaporator 30 maintains the evaporator firsttemperature, providing a user-set evaporator target temperature, andreducing or changing a rate of refrigerant compressed by a compressor 14based on a relationship between the length of time that the evaporator30 maintains the evaporator first temperature and the evaporator targettemperature.

The method may further entail reducing the rate of refrigerantcompressed by the compressor 14 when the length of time that theevaporator 30 maintains the evaporator first temperature is at or abovea predetermined time and greater than the evaporator target temperature.Still yet, the method of control may entail measuring an evaporatorsecond temperature at an exit side of the evaporator, and comparing theevaporator second temperature and the evaporator first temperature, andthen increasing the rate of refrigerant compressed by the compressorwhen the measured evaporator second temperature is greater than theevaporator first temperature.

Reducing a rate of refrigerant compressed by a compressor based on arelationship between the length of time that the evaporator maintainsthe evaporator first temperature and the evaporator target temperaturemay entail reducing electrical energy to the compressor 14 if thecompressor is an electrically powered compressor 14. Alternatively, inthe event that the compressor is not electrically powered, but ratherbelt driven and engaged by a clutch, for example, the length of timethat a clutch of the compressor is engaged, to drive the compression ofthe compressor, may be altered to alter the length of time that thecompressor compresses.

Still yet, an air conditioner control method 80 may entail measuring anevaporator first temperature at an exit side 48 of the evaporator 30,measuring a length of time that the evaporator 30 maintains theevaporator first temperature, providing a user-set evaporator targettemperature, reducing a rate of refrigerant compressed by the compressor14 when the length of time that the evaporator maintains the evaporatorfirst temperature is at or above a predetermined time and greater thanthe evaporator target temperature, measuring an evaporator secondtemperature at an exit side 48 of the evaporator 30, comparing theevaporator second temperature and the evaporator first temperature, andincreasing the rate of refrigerant compressed by the compressor 14 whenthe measured evaporator second temperature is greater than theevaporator first temperature.

The evaporator 30 reaches its cooling capacity when increasing the rateof refrigerant compression does not lower the temperature of theevaporator 30, for instance, at an exit side of the evaporator 30.Additionally, the evaporator 30 may be said to reach its coolingcapacity when, after operating the compressor 14 continuously, theevaporator 30 reaches a temperature measured at an exit side (such as inthe air within approximately three inches of the evaporator exitsurface) or at an exit surface of the evaporator 30 below which a lowertemperature is not possible to achieve. Stated differently, additionalcompression of the compressor 14 such as operating the compressor 14 ata determined rate for extended periods of time (including continuously)or increasing the flow rate of refrigerant compression for a period oftime, does not result in a lower evaporator surface temperature or lowertemperature measured at the exit side of the evaporator 30.

In another control method of an air conditioner, a cold storage unit 112may be utilized. The method may entail terminating operation of an airconditioner compressor 14, such as by turning off an internal combustionengine 16, which powers the compressor 14, maintaining operation of acondenser cooling fan 31, closing a thermostatic expansion valve 28, andopening a bleed port 122 as a bypass of the thermostatic expansion valve28. Furthermore, the air conditioner control method may entail receivingliquid refrigerant into the evaporator 30 from the condenser 22, orreceiving liquid refrigerant into the evaporator 30 from the condenser22 after the liquid refrigerant passes through a bleed port 122 tobypass the thermostatic expansion valve 28. Alternatively, the controlmethod may entail forcing a liquid refrigerant from a condenser 22 at afirst pressure into a cold storage unit 112 at a second pressure, suchthat the first pressure is higher than the second pressure. The liquidrefrigerant may pass through a bleed port 122 that bypasses thethermostatic expansion valve 28 and then into an evaporator 30 beforethe liquid refrigerant is forced into the cold storage unit 112.

In another example of a method of controlling an air conditioner thatutilizes a condenser 22 and a cold storage unit 112, the compressor 14may be turned off, such as by turning off the engine that mechanicallypowers the compressor 14. Upon turning off the compressor 14, thecondenser cooling fan 31 or fans would continue to operate (spin andblow air) to continue to cool the liquid refrigerant 123 within thecondenser 22. Additionally, the closing of a thermostatic expansionvalve 28 would occur and the opening of a bleed port 122 to bypass thethermostatic expansion valve 28 would occur. Opening of the bleed port122 would permit liquid refrigerant to flow through the bleed port 122or passage without having to pass through the TXV 28. Next, because thepressure in the condenser 22, upon turning off the compressor 14, wouldbe higher than that within the evaporator 30 or cold storage unit 112,the condenser 22 would force, due to the higher pressure, a volume ofthe liquid refrigerant 123 in the condenser 22 through the bleed port122, through the evaporator 30, and into the cold storage unit 112. Thatis, the refrigerant would be received in the cold storage unit from thecondenser 22 because of the pressure differential between the condenser22 and the cold storage unit 112 forces such a flow of the liquidrefrigerant 123. Liquid refrigerant would not flow past the cold storageunit 112, such as to the compressor 14, when the compressor 14 is notcompressing.

What is claimed is:
 1. An air conditioner control method utilizing acold storage unit, the method comprising: terminating operation of anair conditioner compressor; maintaining operation of a condenser coolingfan after terminating operation of the air conditioner compressor;closing a thermostatic expansion valve; and opening a bleed port as abypass of the thermostatic expansion valve.
 2. The air conditionercontrol method of claim 1, further comprising: receiving liquidrefrigerant into the evaporator from the condenser.
 3. The airconditioner control method of claim 1, further comprising: receivingliquid refrigerant into the evaporator from the condenser after theliquid refrigerant passes through a bleed port to bypass thethermostatic expansion valve.
 4. The air conditioner control method ofclaim 1, further comprising: forcing a liquid refrigerant from acondenser at a first pressure into a cold storage unit at a secondpressure, wherein the first pressure is higher than the second pressure.5. The air conditioner control method of claim 1, wherein the liquidrefrigerant passes through a bleed port to bypass the thermostaticexpansion valve and then an evaporator before the liquid refrigerant isforced into the cold storage unit.
 6. An air conditioner control methodutilizing a condenser and a cold storage unit, the method comprising:turning off an air conditioner compressor; maintaining operation of acondenser cooling fan; closing a thermostatic expansion valve; opening ableed port to bypass the thermostatic expansion valve; receiving aliquid refrigerant into the cold storage unit from the condenser afterthe refrigerant passes through a thermostatic expansion valve bleed portand the evaporator.
 7. The air conditioner control method of claim 6,wherein receiving the liquid refrigerant into the cold storage unit isgoverned by a pressure in the condenser that is higher than a pressurein the cold storage unit.